Self-routing multipath packet switching networks, such as those using banyan switching nodes, communicate packets through the switching network on the basis of address information contained within the packet or transmitted through the switching network prior to the transmission of the packet. One such system is described in U.S. Pat. No. 4,550,397, by J. S. Turner, et al. The latter describes a system in which switching network nodes automatically determine an alternate route through a switching network so as to increase reliability and distribute traffic. The switching network comprises stages of distribution and routing nodes. The routing nodes are responsive to physical addresses associated with the packets to communicate those packets to address designated downstream nodes. The distribution switching nodes statistically communicate packets to downstream switching nodes on the basis of an alternate routing algorithm and availability of downstream nodes. The initial network stages are alternate distribution and routing stages followed by only routing stages for the remaining stages of the network.
Another switching system that utilizes the address within a packet to route the packet through a multipath switching network is described in the previously mentioned application by C. A. Lea and W. A. Montgomery, Case 2-3. This application discloses a packet switching network in which self-routing packets are communicated through the network by intra-communication of the packets within a stage as well as inter-communication of packets among stages. The stages each have a plurality of pairs of switch nodes with each pair having an intra-node link between the pair of nodes. Each of the switch nodes comprise input controllers and output controllers. The input controller of a node is responsive to the receipt of a packet for interrogating the address field of the packet to determine the destination of the packet. That input controller, on the basis of the destination determination, communicates the packet towards the destination via either an inter-stage link or an intra-node link on the basis of availability of the links and an internal control circuit.
A self-routing multipath packet switching network that uses unbuffered banyan switching nodes to communicate packets through the network on the basis of address information transmitted through the switching network prior to the transmission of packets is described in the previously referenced application by C. A. Lea, Case 1. This self-routing network has a plurality of stages and the stages are interconnected by links. Each pair of switch nodes within a given stage share the same set of input links from the preceding stage. In respronse to the receipt of address information from a destination interface controller transmitted via a link, a pair of nodes determine one of a multitude of paths through the switching network by one of the pair responding to the address information to communicate the address information to the next sequential stage after establishing a path through that particular switch node. Once a path has been established through the switch node, an acknowledge signal is transmitted back from the network to the destinaticn trunk controller indicating that a path has been established. The path remains established until the end field of the packet is detected or the proper end information is transmitted after the transmission of the circuit switched information.
The self-routing multipath switching networks described have the capability of efficiently and rapidly setting up one of a multitude of paths through a switching network to interconnect a given input port to a given output port. However, the rate at which data can be transmitted over this path is limited by the fact that the switching nodes operate in the electronic domain, hence, are only capable of maximum bandwidths of approximately 50 Mbs for a serial stream. It is known to use parallel paths between switching nodes to increase the bandwidth somewhat, but this greatly complicates the interconnection problem between the nodes.
Photonic switching technology is capable of transmitting data at extremely high bandwidths; however, is not well suited for performing the control functiors. The reason why photonic switching technologies have difficulty in performing the control functions is that data path crossovers are very difficult to implement. The reason for this difficulty is that efficient waveguide crossovers require large angles of intersection in order to minimize the interface between adjacent waveguides. Since efficient integrated waveguide crossovers are difficult to fabricate in a photonic technology such as titanium diffused lithium niobate, it is difficult to include control functions. In addition, optical logic devices are difficult to implement and it is uneconomical and time inefficient to translate from the optical to the electrical domain to perform these control functions.
From the foregoing, it can be seen that there exists a need for a switch node that can combine the efficient route selection techniques of an electronic switch node with the data bandwidth of a photonic device. Furthermore, such a switch node should lend itself to utilization in a multipath switching architecture that requires the minimum number of switch nodes so that circuit switching can be performed in the same network that is doing packet switching. In addition to a photonic data path through the network, it is also desirable to maintain an electrical path for the transmission of control and auxiliary data information.